Mar 26, 2025, 22:03:06 UTC• ADN250326F

Study of Exoplanets Using the Transit Method

V. Lipunov, V. Kornilov, E. Gorbovskoy, K. Zhirkov, N. Tyurina, P. Balanutsa, A. Kuznetsov, V. Senik, D. Vlasenko, G. Antipov, D. Zimnukhov, E. Minkina, A. Chasovnikov, V. Topolev, D. Kuvshinov, D. Cheryasov, Ya. Kechin, Yu. Tselik, A. Sosnovskij (Lomonosov Moscow State University, SAI, Physics Department), R. Podesta, C. Lopez, F. Podesta, C. Francile (Observatorio Astronomico Felix Aguilar OAFA), R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias), D. Buckley (South African Astronomical Observatory), O. A. Gress, N. M. Budnev, O. Ershova (Irkutsk State University, API), L. Carrasco, J. R. Valdes, V. Chavushyan, V. M. Patino Alvarez, J. Martinez, A. R. Corella, L. H. Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), V. Yurkov, A. Gabovich (Blagoveschensk Educational State University)

Light curve

Band

optical

T	23:00:00	23:00:00⁺¹	23:01:00⁺²
T−T0	0	86,400 s	172,860 s
mag.	1^m	1^m	1^m
limit	1^m	1^m	2^m
exp.	1 s	1 s	3 s
filter	▨ I	▨ I	▨ I
RA	0^h 04^m 00^s	0^h 04^m 00^s	0^h 04^m 00^s
Dec.	+2° 00′ 00″	+2° 00′ 00″	+2° 00′ 00″
err.	3°	3°	3°
inst.	SAI MSU	SAI MSU	SAI MSU

The study of exoplanets is one of the key tasks of modern astronomy. Exoplanets are planets that exist beyond our Solar System and orbit other stars. One of the most effective methods for their detection is the transit method, which is based on recording the decrease in a star's brightness when a planet passes in front of it.

Modern space telescopes such as Kepler, TESS, and the James Webb Space Telescope (JWST) use the transit method to search for and study exoplanets. This method allows not only the discovery of new planets but also the analysis of their physical properties, such as radius, density, and atmospheric composition.

The Transit Method

Basic Principles

The transit method involves measuring the decrease in a star's brightness when an exoplanet passes across its disk. The fundamental equation describing the transit depth is:

\Delta F = \left(\frac{R_p}{R_*}\right)^2

where:

$\Delta F$ — relative decrease in the star's brightness,
$R_p$ — radius of the planet,
$R_*$ — radius of the star.

The accuracy of measurements depends on the characteristics of the telescope and the observing conditions. The larger the planet relative to its star, the greater the dimming and the easier it is to detect. However, small planets, similar to Earth, are harder to observe due to the minimal brightness changes they cause.

Examples of Observed Parameters

Parameter	Value
Star radius ( $R_*$ )	$1.0 R_\odot$
Planet radius ( $R_p$ )	$1.3 R_\oplus$
Transit depth ( $\Delta F$ )	0.00017 (or 0.017%)
Orbital period ( $P$ )	3.5 days

Applications of the Method

The transit method is widely used not only for detecting planets but also for determining their characteristics. For example, if scientists observe multiple transits of the same planet, this allows them to:

Determine the orbital period (the time it takes for the planet to complete one revolution around the star).
Calculate the orbital eccentricity (how elongated or circular the orbit is).
Study the planet's atmosphere using spectroscopy by analyzing the changes in the light spectrum during transit.

Discovery of Exoplanets

Thousands of exoplanets have been discovered using the transit method, including well-known systems such as TRAPPIST-1, which contains seven Earth-like planets, and Kepler-186, the first system where a potentially habitable exoplanet was found in the habitable zone (NASA Exoplanet Archive).

Additionally, this method allows the classification of exoplanets based on their size and composition. For instance, exoplanets are categorized as:

Super-Earths — planets with a radius 1 to 2 times that of Earth.
Mini-Neptunes — planets with a gaseous envelope but smaller than Neptune.
Gas Giants — similar to Jupiter and Saturn in size and composition.

With advancements in technology, exoplanet detection methods continue to improve, and future missions such as PLATO (ESA) will allow the discovery of even more new worlds.

Conclusion

The transit method remains one of the most powerful tools for detecting exoplanets. In combination with other methods, such as the radial velocity method, it provides crucial data on the mass, density, and atmospheres of exoplanets.

Thanks to advancements in observational astronomy, the number of discovered exoplanets continues to grow, expanding our understanding of planetary system formation and the potential conditions for life beyond Earth. In the future, even more detailed studies of exoplanetary atmospheres and possibly the first signs of extraterrestrial life can be expected.

References

ADN220903
10.1109/5.771073
GCN 36060